Satellites broadcast signals that may be used for navigation and which may include measurements of position and/or time that may alternatively be used for these specific applications. Signals broadcast from Global Positioning System (GPS) satellites, Global Navigation Satellite System (GLONASS) satellites, BeiDou Navigation System (COMPASS) satellites, and Galileo satellites are designed to be used for navigation. Signals from other satellites, while not specifically designed for navigation, may also be used for navigation. This may include at least one satellite such as a low earth orbiting (LEO) Iridium satellite or a GlobalStar satellite.
In such satellites and/or satellite systems, consistent timing of signal transmission is required for accurate satellite navigation. In particular, a consistent time delay due to the signal path is desired. This refers to the time a signal is generated by a signal source inside a satellite until the time the signal is transmitted by a transmit antenna on the satellite. In satellite systems that are designed to be used for navigation, care is taken to ensure the time delay is, to a large extent, constant or that it changes very slowly over time, since time delay variations introduce an error in the accuracy of the time of arrival measurements at a receiver of signals transmitted by the satellite.